Assessing the risk of small disturbance instability in mixed AC/DC networks

This paper presents a risk-based Probabilistic Small-disturbance Security Analysis (PSSA) of a mixed AC/DC power system. The proposed approach establishes the probability density functions (pdfs) for the critical system modes based on the stochastic variation of operational system uncertainties (such as generation, loading, and HVDC line power flows). From these pdfs the probability of unstable operation or poorly damped oscillations in the system is determined. This analysis can be completed for any given loading scenario and level of uncertainty. Furthermore, the approach is utilized to establish risk-based power flow limits to ensure acceptable system performance.